1. Field of the Invention
The present invention relates to technology for correcting shape defects in samples having fine stencil structures such as stencil masks for Electron beam Projection Lithography (EPL).
2. Description of Related Art
Increases in the level of integration in LSI""s and systemization have led to the possibility in recent years of small, highly functional electronic equipment such as personal computers and mobile telephones. Circuit patterns are drawn with a few million elements packed onto a semiconductor chip of a few millimeters in every direction so as to have a line width from a micron order to a nano-order and development of lithographic technology for implementing this is expanding. Until now, the main focus of lithography has been optical lithography technology. There, the wavelength of light used is taken to be extremely short to correspond to the fine detail of the pattern, and short wavelength lasers were used. This processing has also, however, encountered problems with the optical systems and the resists and compatibility of the optical exposure devices with fine detail is also reaching its limit. Much is therefore expected from technology for replacing light with a source such as an electron beam or ultra-short-wave ultra-violet light. mask for electron beam exposure used in lithography taking an electron beam as a source can be determined using exposure tests using an actual exposure device or observing a transmission image of an electron beam device such as an electron microscope. Defects are corrected in electron beam exposure masks in which defects have appeared using the elimination of foreign bodies that have become attached (black defect correction) utilizing an etching function of a Focused Ion Beam (FIB) device and by using additional defect portion processing (white defect correction) utilizing an ion beam induction deposition function. Further, the surface (sample surface) of a mask for electron beam exposure is irradiated with and scanned by a focused ion beam so that secondary charged particles (for example, secondary electrons, secondary ions etc.) emitted from the sample surface are detected by a secondary charged particle detector positioned to the front of the sample surface (ion source side). A scanning ion microscope (Scanning Ion Microscope: SIM) image is then obtained from the information for the sample surface, and the location and shape of the defects is determined. The appearance of the advancement of the processing is monitored, the shape after implementation of defect correction is confirmed, and a determination is made as to whether or not the target processing is complete.
However, it is necessary for the electron beam exposure mask to have a certain degree of thickness in accordance with the energy of electron beams used in exposure and the material of the electron beam exposure mask in order that the electron beam exposure mask is impermeable with respect to an electron beam. An opening for allowing an electron beam to pass is made narrow in order to provide compatibility with the fine detail of the exposure pattern rule. The dimension of the thickness with respect to the width is therefore an ultra-fine stencil structure of a high aspect ratio. As the aspect ratios of structures increase, defect portions that are at deep portions from the surface of the opening are such that secondary electrons generated by the ion beam irradiation do not easily reach a detector so that sufficient electrons are not caught and it is therefore difficult to observe an SIM image from the surface direction. Namely, it is difficult for secondary electrons from a deep hole or from the bottom of a deep channel to reach a detector via an opening in the mask surface, and it is difficult to reliably determine the shape of the defect correction portion from a related SIM image. Because of this, it is not possible to reliably confirm the finished shape of deep portions and remaining fragments of material that should have been removed therefore occur.
With ion beams where particle diameter and mass are large, and electron beams where these properties are small, transmission characteristics with respect to the sample (electron beam exposure mask) differ. Therefore, even with technology for accurately comprehending three-dimensional defect structures utilizing the fact that it is possible for ion beams to cause secondary electrons to be ejected from deeper portions of material, or with technology for carrying out three-dimensional evaluation (scanning) of defect correction results, or for scanning deep portions of a thick sample (ultra-fine stencil structure) with a high aspect ratio, this is difficult while only monitoring an SIM image from the surface direction. Because scanning and confirmation of the shape after correction of the electron beam exposure mask that has been subjected to defect correction using FIB by microscopic observation using the same FIB device is difficult for the reasons given above, evaluation scanning (exposure shape, projected image, confirmation of surface shape using SEM image) using other electron beam devices such as exposure devices and transmission electron microscopes (TEM), or scanning electron microscopes (SEM) etc. is carried out. However, repeating a cycle of correction and scanning between these devices involves a complicated and troublesome procedure where the sample is extracted from the vacuum chamber of one device and moved to a chamber of another device, the environmental conditions are adjusted, positioning alignment is carried out, and processing and scanning is then implemented. There is also the fear that new defects will occur as a result of dirt becoming attached as a result of the movement of the sample.
Further, in the case of scanning using the electron beam, it is necessary to observe both an SEM image for observing surface shape and a transmission image corresponding to a projected image for the opening. It is therefore necessary for the electron beam to be incident to the mask surface from an orthogonal direction. As the electron beam is incident perpendicular to the electron beam exposure mask surface, with, for example, devices such as a related FIB-SEM dual device shown in FIG. 10A where an FIB lens barrel 1 and SEM lens barrel 11 are fitted at a certain angle (for example, 55 degrees), when changing between correction (FIG. 10A) and scanning (FIG. 10B), as shown in the drawings, it is necessary to incline the stage at a substantial angle, and even in a situation where the FIB lens barrel 1 and the SEM lens barrel 11 are separated by a certain distance so as not to interfere with each other as shown in FIG. 10C, it is necessary to move the stage 30 substantially in the horizontal direction from the situation during correction in FIG. 10C to the situation during scanning in FIG. 10D. These related dual FIB-SEM devices are advantageous from the point of view of dirt becoming attached and the shortening of the operation time because it is not necessary to move the sample between the devices. However, also with regards to the ion beam for correcting defects, in order to achieve perpendicularity of wall surfaces after processing, it is necessary for the ion beam to be precisely vertically incident with respect to the mask surface and substantial movement of the sample stage is therefore necessary, which is disadvantageous with respect to processing accuracy.
In order to resolve the aforementioned problems, the present invention provides a focused ion beam device capable of not only performing processing to correct defects in an electron beam exposure mask of an ultra-fine stencil structure, but also capable of observation of microscopic images of defect portions for portions that are deep portions from the surface of an opening.
In accordance the present invention, there is provided a fine stencil structure correction device characterized by a device for irradiating and scanning with a charged particle beam so as to correct shapes of defects at locations of a fine stencil structure sample using an etching and/or deposition function, where means for detecting a transmitted beam is located on the opposite side of the sample as viewed from the beam source. An absorbed current detector or a combination of a transmitted beam target and a secondary charged particle detector can be adopted as the detection means.
Further, after processing using an FIB, lens barrels for a Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscope (STEM) and a Transmission Electron Microscope (TEM) can be the same FIB lens barrel and be located in the same vacuum chamber in order to confirm processing results without it being necessary to move the fine stencil structure sample outside of the device. This keeps movement of the sample extremely small. Further, a transmission electron microscope function is provided as a primary beam for observation, and a projection plate such as a fluorescent plate etc. for enlarging and projecting transmitted electrons can be adopted as means for detecting a transmitted beam located to the rear of the sample.
The primary beam for use in processing and the primary beam for use in observation are arranged facing each other so as to sandwich the fine stencil structure sample. Each detector for each transmitted beam is retracted when not in use so as not to irradiate a beam to the other detector.
The means for detecting a transmitted beam located to the rear of the sample functions both as an absorbed current detector and a beam target for emitting secondary electrons, and has three positions for ensuring there is no obstruction to other beam emissions or to switching these functions over.